Project Information

Summary:

A comparison of different acid-tolerant ground covers in highbush blueberry determined that row middle covers influence the abundance of Japanese beetle, Popillia japonica Newman, (Coleoptera: Scarabaeidae) adults and larvae. Buckwheat was more attractive to adults, but fewer larvae were found in these plots compared to ryegrass and clover. More Japanese beetles were found in all planted row middles than those with bare ground. Most timings of row-middle cultivation caused a reduction in P. japonica larval density, although patterns were not consistent across two years. These results indicate that cultural control can reduce the likelihood of P. japonica becoming established in fields, and that cultivation and cover crops should be integrated into perennial fruit production to minimize the potential for economic impact by this pest. Results of the research were presented to blueberry growers at summer and winter meetings and a fact sheet has been published to inform growers of the latest research results on Japanese beetle management.

Introduction:

The Japanese beetle, Popillia japonica Newman, (Coleoptera: Scarabaeidae) is an invasive insect with potential for range expansion into many of the major agricultural production regions of the USA (ALLSOPP, 1996). P. japonica is currently the most important pest for producers of highbush blueberry, Vaccinium corymbosum L., in the Midwestern United States (ANON., 2001; ISAACS et al., 2004). It is a univoltine insect, with greatest adult abundance from mid-July to August (FLEMING, 1972), when beetles feed on leaf tissue and ripe blueberry fruits. If beetles are not controlled, fruit can be contaminated when harvesting machines knock beetles off the bushes. Over 70% of Michigan’s 7,285 ha of blueberry crop is harvested mechanically (KLEWENO and MATTHEWS, 2002), and because the market demands fruit completely free of insect contamination, strategies are needed to minimize the risk of adult beetles being present during harvest. Foliar insecticide applications continue to be the foundation of P. japonica management in blueberries and many other fruit crops, as growers strive to meet exacting quality standards. Additional strategies targeting larvae, which develop in the soil, may help growers reduce populations of P. japonica within infested blueberry production regions and minimize the risk of beetles spreading into uninfested areas. Such strategies could also have the long-term benefit of reducing the number of foliar applications of insecticides.

Project Objectives:

Test the impact of acid-tolerant cover crops on Japanese beetle establishment in blueberries.

Investigate the effect of cultivation timing on larval density in row middles of blueberry.

Demonstrate sustainable approaches of Japanese beetle suppression to the blueberry industry.

Cooperators

Research

Materials and methods:

The experiments to examine P. japonica larval density and adult abundance were conducted at the Trevor Nichols Research Complex in Fennville, MI. A 4047 m2 highbush blueberry planting (V. corymbosum var. Bluecrop) was established in 2001, on a 3.7 m x 1.4 m plant spacing with 12 bushes in each row. The cover crop treatments were seeded in the row middles (53 m2 / row middle) in May and June 2002 in a completely randomized design. The four treatments were perennial ryegrass (Lolium perenne L.), alsike clover (Trifolium hybridum L.), buckwheat (Fagopyrum esculentum Moench) and control row middles were left without vegetation. Treatments were replicated five times. The seeds for the cover crop treatments were sown by hand in the two row middles on either side of a row of blueberry bushes, and compacted into the soil using a tractor-pulled roller. Seeding rate for perennial ryegrass was 27 kg/ha, for clover 22 kg/ha, and for buckwheat 67 kg/ha (Michigan State Seed Solutions, Grand Ledge, MI). The bare ground plots received treatments of herbicide (Roundup Ultra 4WSL at 31.3ml/l) spot-applied with a 3.78 l hand-held sprayer when needed, to keep the soil free of vegetation during the growing seasons. Overhead irrigation of all the row middles was started from the time of seeding, and was done weekly or as needed throughout the growing season in each of the years of this study to create conditions typical of a commercial blueberry field.

Objective 1. Test the impact of acid-tolerant cover crops on Japanese beetle establishment in blueberries.

Japanese beetle larval density was surveyed by taking soil samples before the seeds were sown in the plots. Larval density was sampled in October 2002, May and September 2003, and in May and September 2004 by taking five 15 cm deep soil cores from each row middle. This was done using a cylindrical golf cup cutter (area = 95 cm2) (Parmenter & Andre Inc., Grand Rapids, MI). Soil cores were examined in the field, and all beetle larvae were placed in plastic bags with a small amount of soil. The bags were labelled with date, treatment, and number of larvae and transported back to the laboratory in a cooler containing an icepack. Larvae were identified to species using the diagnostic rastral patterns and other morphological features. The five larval samples from each row middle were averaged and compared among the treatments. Data were transformed (√y+0.1) and analysed with PROC GLM with LSD means separation, α = 0.05 (SAS, 2001).

P. japonica adults were visually surveyed in each of the row middles, weekly in July and August in 2002, 2003, and 2004. Observations were conducted from 12 – 2 PM on sunny days, with low wind conditions. Visual survey of each row middle lasted two minutes during which time the observer walked down one side of the row middle and back on the other side, always focusing on the cover crop and keeping track of the number of beetles. The observer walked on the periphery of the area covered by the crops, wore neutrally colored clothes, and moved evenly and slowly so as to minimize the disturbance of the beetles by the person, as they are mobile and easily disturbed. At the end of the two minutes the number of beetles seen on the cover crops was recorded on a data sheet. Adult counts were analysed with Proc GLM, with date as block in the model, and means were compared with the LSD method (SAS, 2001). The critical value for significance for all these tests was determined at α = 0.05 level.

Objective 2. Investigate the effect of cultivation timing on larval density in row middles of blueberry.

The experiment to test the effect of cultivation timing in infested plots was conducted in two 0.07 ha sections of a 1 ha field of V. corymbosum cv. Rubel, at the Trevor Nichols Research Complex, Fennville, MI. The blueberry plants were 10 years old on a 3.6 x 1.2 m plant spacing, with 12 bushes in each row. The 14 x 2.5 m row middles between the rows of blueberry were comprised of naturally occurring weeds dominated by grass species, and were kept mowed. The experiment was conducted in 21 adjacent row middles in 2002 and the experiment was repeated in 2003 in 21 adjacent row middles located in a different section of the same blueberry field. These two sections of the field were selected based on prior sampling to verify the presence of P. japonica larvae across the field sections. The following three treatments were applied during both years to the different sections: rotovation once in the spring, rotovation once in the autumn, or rotovation once in the spring and once in the autumn. Treatments were assigned to the row middles in a completely randomised design with seven replicates. To cultivate plots, a tractor-powered BushHog rotovator (Model H72, Allied Products Corporation, Selma, Alabama) was driven between the bush rows twice, at 15 cm depth. Plots that were rotovated in the spring were kept weed free in the growing season by applying herbicide (as described above). Rotovation was on May 10 and September 9 in 2002 and on May 2 and Oct 10 in 2003. All plots were sampled with a golf cup cutter as described above, before rotovation in both the spring and the autumn, and rotovated plots were sampled after cultivation. P. japonica larvae were sampled 2-4 days before and 10-14 days after rotovation treatments. Three samples were taken per row middle in 2002 and six in 2003, and collected larvae were identified to species. Larval count data were not normally distributed, so pre- and post-rotovation densities were compared with a Wilcoxon two-sample test. Comparison of the percent reduction in P. japonica density between treatments was done after arcsine transformation with a one-way ANOVA procedure followed by Tukey’s means separation at α = 0.05.

Objective 3. Demonstrate sustainable approaches of Japanese beetle suppression to the blueberry industry.

Extension meetings were held at the research plot for Michigan blueberry growers in 2003 and 2004, with each meeting attended by ~40 growers. We also demonstrated the research to the Michigan Agricultural Experiment Station leadership council in 2004, to the MSU International Agriculture class in 2003 and 2004, and the MSU Fruit Area of Expertise Team annual meeting in 2004.

Results from the research were used to inform our preparation of a factsheet, published by MSU Extension as part of the Blueberry Facts Series:
Isaacs, R., Szendrei, Z. and Wise, J. (2003) Japanese beetle. Michigan State University Extension Blueberry Facts Bulletin E-2845. 4 pp.

Research results and discussion:

Bare ground row middles had the fewest larvae on average throughout the study. Buckwheat had significantly more larvae than bare ground, but there were significantly fewer larvae compared to ryegrass and clover. Ryegrass had the highest number of P. japonica larvae consistently in this study. Clover and ryegrass had very similar numbers of larvae on average, except for spring 2004, when there were significantly fewer larvae in clover than ryegrass. Buckwheat was successful in reducing P. japonica larval density compared to ryegrass and clover. This could be because gravid females do not recognize this plant as a potential oviposition resource or because larval survival is lower than in clover and ryegrass.

Adult P. japonica were significantly more abundant in buckwheat throughout this experiment than in any of the other treatments. There were significantly fewer adults in clover than in buckwheat in 2002 and 2003. Bare ground had consistently the lowest number of adults, in all years. In 2003 there were significantly more adults in ryegrass than in bare ground, but in the other two years, ryegrass was not significantly different from bare ground. Adult densities were lowest in ryegrass and bare ground row middles. These results, along with the larval density data imply that there are potential cover crops that are suitable for cultural control of P. japonica larvae (buckwheat), but which are attractive for adults. In contrast, others are not attractive for the adults (ryegrass), but have the greatest larval density.

In the small plot trials, cultivation in row middles proved to be effective in preventing the establishment of P. japonica larval populations. Rotovation both in the spring and fall in row middles proved to be effective in this study in reducing larval populations by 59%. The change in P. japonica larval abundance due to cultivation in the spring was not consistent over the two years; this treatment caused a significant decline in larval density in 2003, but not in 2002. Cultivation in the autumn caused a decrease in P. japonica during both years when comparing pre- and post-rotovation larval densities, but this trend was only significant in 2003. Rotovating the same plot twice, in the spring and in the autumn, significantly reduced larval density in both years, when comparing overall reduction from spring to fall, by 50.5 ± 11.45 % in 2002 and 68.8 ± 14.6 % in 2003. Most of the treatments caused a similar reduction in P. japonica larval density in the row middles and the percent control values were not significantly different in either year.

Educational & Outreach Activities

Participation Summary

Szendrei, Z. and R. Isaacs. Effect of cultural practices on the oviposition behavior of the Japanese beetle (Popillia japonica, Coleoptera: Scarabaeidae). 51st Annual Meeting of the Entomological Society of America, Cincinnati, OH, USA, October 2003. Presentation.

Isaacs, R., Z. Szendrei, and J.C. Wise. Evaluation of new approaches for management of Japanese beetles in highbush blueberries. 9th North American Blueberry Research and Extension Workers Conference, Halifax, NS, Canada, August 18-21, 2002. Presentation.

Project Outcomes

Project outcomes:

Farmer Adoption

Blueberry growers in Michigan have shown interest in trying new cover crops. Some growers have already seeded clover in their fields and others are looking at the new findings to determine how cover crops may be integrated into their production system. The high degree of control of Japanese beetle by cultivation seen in this project has led to widespread increase in cultivation to reduce the likelihood that blueberry fields are suitable habitats for P. japonica. Although this is a non-chemical management technique, it brings up issues such as soil erosion that suggest the search for effective cover crops should continue. Based on the findings of this project, further research will start in 2005 as a collaboration between Dale Mutch, Rufus Isaacs, and Eric Hanson, to evaluate cover crops at a commercial blueberry grower’s farm.

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.

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